Great topic, very important. I am a lawyer and you did a good summary. Typically the amount of money involved in a roleplaying game is so minimal that actual litigation isn't advisable to anyone who will ever read a web forum. However, you never know what will hit big and you definitely should keep an eye on what you own and what you don't or can't. Specifically, here, I'm thinking of game mechanics as different from the fixed expression of game mechanics. It's actually quite hard (and half-untested - a long story) to patent game mechanics as a process. But you can obtain copyright on expression that you do of game mechanics (texts, etc.)